Phomopsis subordinaria field survey
To characterize the distribution, and drivers, of P.
subordinaria, and to measure the relationship between within-host
symptom severity and epidemic size and within-population prevalence, we
surveyed 260 P. lanceolata populations in early September 2018
for infection by P. subordinaria . These populations were selected
to represent different areas in the Ă…land Islands. The field
identification of P. subordinaria was confirmed by microscopy of
field collected samples consisting of an infected floral stalk. In each
population, the epidemic size (measured as number of infected plants),
and within-population prevalence (measured as proportion of infected
plants within-population) of P. subordinaria infected plants was
counted. In each population, we assessed the within-host infection load
of the pathogen by counting the proportion of infected flower stalks
within each plant from ten infected plants. Host population size is
expected to increase infection risk of populations (Parratt et al.,
2016) and thus, we estimated the host population size as coverage of the
host plant in square meters. Host connectivity was measured in order to
understand how distances between host populations may impact pathogen
prevalence (Jousimo et al., 2014). Host population connectivity was
calculated as